Induction motors have conventionally been known that include a stator that produces a rotating magnetic field and a rotor that is provided inside the stator and rotates in accordance with the rotating magnetic field. The induction motors are classified into two types depending on the types of alternate current to be supplied: single-phase induction motors; and three-phase induction motors. Of these induction motors, the three-phase induction motors have been widely used as general-purpose motors.
Such a three-phase induction motor includes a rotor formed of thick copper wires (bars) arranged in a cage shape. The rotor includes an iron core, a plurality of copper wires and end rings. The rotor is manufactured such that the copper wires are inserted into insertion holes of the iron core that is built with stacks of steel sheets, and both ends of each copper wire are fixed to the respective end rings (see Patent Literature 1, for example).
In Patent Literature 1, the copper wires are fixed to the end rings by friction stir welding. Friction stir welding is a joining process that can be performed with reduced cost compared to other joining processes such as brazing.